New design methodologies for printed circuit axial field brushless dc motors

Abstract

[Abstract] A number of factors are contributing to the increased practical importance of printed circuit axial flux brushless direct current (BLDC) machines. The main ones are the availability of low cost power electronic devices and digital controllers as well as cost effective high strength permanent magnets. Advancement of multi-layer printed circuit technology is also an important factor. Existing printed circuit board motors, found in applications such as computer disk drives and portable audio-visual equipment, are typically rated at a few watts per thousand revolutions per minute (krpm). The focus of this thesis project has been on printed circuit motors with ratings of a few tens of watts per krpm. A significant part of this thesis project has been devoted to development of systematic design procedures for printed circuit stators. In particular those procedures include algorithms which allow performance comparisons of several stator coil shapes. A new coil shape, with improved torque capability, has been developed. BLDC motors that operate in sensorless mode has advantages such as lower cost, better reliability and space saving. A new generalised version of the previously reported equal inductance method has been developed which allows sensorless commutation of printed circuit BLDC motors down to zero speed and start-up with practically no back rotation. Computer efficient numerical models have been developed to predict phase inductances and stator eddy-current loss. Sufficiently accurate phase inductance predictions make possible theoretical assessment of performance of motors under sensorless commutation control that is based on the equal inductance method. The proposed method of calculation of eddy current loss allows designers to determine the track width beyond which eddy current loss becomes excessive. The mathematical model on which the enhanced equal inductance method is based and those that have been used for performance assessment, inductance prediction and eddy-current loss evaluation have all been validated by specially designed laboratory tests carried out on prototype motors.